Adhesive compositions including one or more polymers are often used in the manufacture of medical products that are designed for use in contact with human skin. Adhesive wound dressings may include components to cover a wound, absorb fluids and/or deliver medicaments to the injured skin. Such dressings typically include an adhesive backing which may be applied directly to the skin to maintain the dressing in place over the injury. Additionally, transdermal patches have become an accepted means for the delivery of certain molecules through the layers of the skin, thus eliminating the need for injections. Transdermal patches include a drug dosage which may be stored in an appropriate medium and affixed to an adhesive coated backing. The backing on the transdermal patch is intended to be adhesively affixed to an area of human skin to place and hold the drug-carrying medium in direct contact with the skin and thereby promote the delivery of the drug through the skin. In some instances, the drug dosage may be directly incorporated into the adhesive used to secure the patch to the skin. Adhesive compositions used for securing medical products to human skin are preferably free of significant concentrations of unreacted materials such as residual monomer components, initiator materials, inhibitors or other agents. In addition to enhancing the adhesion, cohesion, stretch and/or adhesive tack of the adhesive, a low level of significant impurities in such adhesive formulations is also desired to avoid certain unwanted features in the final product, such as unpleasant odors or the like.
Adhesive polymers that have been prepared by conventional free radical solution polymerization generally include impurities, such as residual monomers, initiator materials, inhibitors or other agents. Although residual monomers may be removed from the adhesive polymer by use of scavenger (or scavenging) monomers, this method also requires the removal of the scavenger monomer and the polymers that result are generally not the same as the original adhesive polymer obtained during the primary polymerization reaction. Alternatively, impurities remaining after free radical solution polymerization may also be removed by multiple heating and evaporation steps which remove volatile components. But, this method may crosslink, gel or degrade the polymer and it is time consuming, costly, and relies upon the volatility of any impurities.
There is a need to provide clean, adhesive polymers prepared by free radical solution polymerization and to improve the ability to remove impurities from such adhesive polymers.